From the past, FM reception devices that receive and process FM (Frequency Modulation) broadcast airwaves and reproduce their broadcast contents have been widespread. Radio waves on the VHF band that are employed as FM broadcast airwaves of this type are reflected by buildings and so on. As a result the multipath phenomenon occurs in which, one or more waves reflected by buildings and so on are received by the FM reception device in addition to the direct FM broadcast wave.
When such a multipath phenomenon occurs, the quality of reproduction of the broadcast contents is deteriorated due to multipath fading because of interference between the direct wave and the reflected wave or waves. In particular, if the FM reception device is mounted to a mobile object such as a vehicle or the like, then it is often used in an environment easily influenced by the multipath phenomenon to be experienced.
Due to this, techniques of various types have been proposed for reducing the influence of multipath fading. One such technique that has been proposed has been the technique of, along with employing a digital adaptive filter for the FM reception device that has the beneficial effect of suppressing the influence of multipath fading, also using either an IIR (Infinite Impulse Response) type adaptive filter or an FIR (Finite Impulse Response) type adaptive filter, depending on the field intensity of the received wave of the FM broadcast airwave (hereinafter referred to as the “received FM wave”) (refer to Patent Document #1, hereinafter referred to as the “prior art example”).
In the technique of this prior art example, if it is decided that the field intensity of the received FM wave is greater than a predetermined threshold value, so that the influence experienced due to multipath fading becomes great, then the IIR type adaptive filter is selected. Moreover, if it is decided that the field intensity of the received FM wave is lower than the predetermined threshold value, so that the influence of flat fading becomes great, then the FIR type adaptive filter is selected.